1. Field of the Invention
The present invention relates to a detection apparatus, an exposure apparatus, and a device fabrication method.
2. Description of the Related Art
An exposure apparatus is employed to fabricate semiconductor devices. The exposure apparatus projects and transfers a circuit pattern formed on a reticle (mask) onto, for example, a wafer (substrate) by a projection optical system. In recent years, an exposure apparatus needs to fabricate not only one-dimensional IC chips such as semiconductor memories and logic circuits, but also special devices such as three-dimensional multilayer chips and MEMSs. The fabrication of such special devices requires less line width resolution and overlay accuracy but requires a larger depth of focus than the fabrication of one-dimensional IC chips.
Also, an exposure apparatus performs a special process to expose the upper surface of a wafer (for example, an Si wafer) based on alignment marks formed on the lower surface side of the wafer. This process is necessary to form a through-hole via from the upper surface side of a wafer to its lower surface side, thereby connecting the former side to a circuit on the latter side. Under the circumstance, Japanese Patent Laid-Open No. 2002-280299 proposes a technique for forming an alignment detection system on the lower surface side (wafer chuck side) of the wafer to detect the alignment marks on the lower surface side of the wafer.
Unfortunately, an alignment detection system formed on the lower surface side of the wafer can detect only alignment marks that fall within a specific region (that is, the detection region of the alignment detection system). In other words, the conventional technique cannot detect alignment marks placed at arbitrary positions on the wafer. Also, an alignment detection system of an exposure apparatus needs to detect not only alignment marks on the lower surface side of the wafer but also those on the upper surface side of the wafer.